Parabolic torus transreflector antenna

Abstract

The parabolic torus transreflector antenna is a circularly symmetric antenna which can be scanned through 360° by rotation of its feed alone. The reflector consists of a radome carrying 45° angled wires so that 45° polarised radiation is reflected on one side and transmitted by the other. A theoretical model has been developed to predict the radiation properties of this antenna for various feed configurations. An experimental torus has been constructed and tested, showing good agreement between theory and experiment. Good radiation patterns (sidelobes ≤ – 20 dB) are obtained with limited aperture efficiency (about 25% of the horizontal aperture). The theory shows how the phase aberrations and amplitude distortions in the radiating aperture, due to the antenna geometry, limit the sidelobe performance for wider aperture illuminations with a single horn feed. A linear array feed, designed to correct phase aberrations in one plane, is found to offer only a partial improvement if the full vertical aperture is required. It is concluded that greater aperture efficiency (≃45%), with sidelobes ≤ – 20 dB, requires either a torus with a restricted vertical aperture, (≤5 λ0), or a planar array feed.